Eh, it's the start of a negotiation. It "gets the mule's attention", and if they were thinking of giving you single digits of equity as I gather is not uncommon you've saved yourself time.
It also demands respect. They may not give it to you, but if something actually happens you'll be starting on the right foot, and the author claims this does not turn everyone who approaches him off.
It also gets the big issues right out there: how much is an idea and anything else they're bringing to the table worth vs. how much is the technical effort to make it live.